The present invention generally relates to Computed Tomography Angiography (CTA)/Electron Beam Angiography (EBA). In particular, the present invention relates to cardiac cine imaging using CTA/EBA.
Medical diagnostic imaging systems encompass a variety of imaging modalities, such as x-ray systems, computerized tomography (CT) systems, ultrasound systems, electron beam tomography (EBT) systems, magnetic resonance (MR) systems, and the like. Medical diagnostic imaging systems generate images of an object, such as a patient, for example, through exposure to an energy source, such as x-rays passing through a patient. The generated images may be used for many purposes. For instance, internal defects in an object may be detected. Additionally, changes in internal structure or alignment may be determined. Fluid flow within an object may also be represented. Furthermore, the image may show the presence or absence of components in an object. The information gained from medical diagnostic imaging has applications in many fields, including medicine and manufacturing.
Angiography refers to techniques for imaging arteries in a body. Coronary arteries of the heart are some of the more significant arteries that are commonly imaged. Problems with coronary arteries account for a large percentage of deaths in the United States each year. Coronary arteries are difficult to image because coronary arteries move with a cardiac cycle with speeds of up to 20 millimeters per second. Observing motion of the coronary arteries may be helpful in diagnosing illnesses or defects.
During the past several years, CTA and EBA were developed to replace invasive coronary angiography. Coronary angiography uses direct injections of contrast media into the coronary arteries using a long catheter. CTA and EBA, on the other hand, use a less invasive approach of a simple intravenous injection of a contrast agent. Current methods obtain CT images of the coronary arteries at specific phases of the cardiac cycle. Since the CT images are obtained at a specific phase of the cardiac cycle using current methods, the CT images are stationary images. The stationary images form cross sectional CT images of coronary arteries. The cross section CT images may be combined to form a spatially three-dimensional image. The cross section images may be combined using techniques such as maximum intensity MIP, Volume Rendering (VR), Shaded Surface Display (SSD), or other types of image processing. The resulting three-dimensional image illustrates a stationary volume at one instant in time.
The images are formed from data acquired during a series of scan. In order for useful data to be acquired in a scan, data acquisition has been synchronized with the cardiac cycle. Gating refers to synchronizing data acquisition with the cardiac cycle. A wave of an electrocardiogram (ECG) may be used to “gate” or synchronize acquisition data with the cardiac cycle. There are two common types of gating, namely prospective and retrospective gating. Prospective gating triggers the start of axial scanning by monitoring the patient's ECG wave and anticipating a chosen point in the interval between R-wave peaks (R-to-R interval) in an ECG cycle. The chosen point may be selected to correspond to the region of the cardiac cycle where cardiac motion is at a minimum. Retrospective gating uses continuous scanning and selects particular images based on the ECG wave information. Conventional systems use retrospective gating for single static images.
Several conditions impact scanning and image acquisition. A typical patient may hold his or her breath for about 45 seconds. To minimize motion artifacts and generate an accurate image, it is preferable in conventional systems that an entire image series be scanned during one breath. Thus, a need exists for an imaging system that may capture imaging data fast enough to scan an entire series of cardiac images in one breath. Additionally, heart rates vary from patient to patient such as from about 50 beats per minute (slow), or 1.2 seconds/heartbeat, to about 120 beats per minute (pediatric), or 0.5 seconds/heartbeat. Current systems are incapable of easily adjusting for multiple or varied heart rates. The inability to adjust for multiple heart rates may result in image artifacts or in an inability to capture properly image data. Thus, there is a need for an imaging system that supports a full range of heart rates.
Further, a particular patient's heart rate may vary during an imaging series. For example, a heart rate may start at about 70 beats per minute, then reduce to 60 beats per minute when a patient first holds his or her breath, and then increase to 90 beats per minute at the end of a patient's ability to hold his or her breath. Also, a particular patient's heart rate may change from one heartbeat to another heartbeat due to stress and other factors. A changing heart rate may introduce motion artifacts or other image artifacts into the obtained images. Thus, there is a need to accommodate a changing heart rate. Furthermore, there is a need to detect irregular heartbeats.
Motion of a table or other apparatus used to position a patient may cause discomfort to a patient. Fast motion of a table may be uncomfortable to a patient and may also cause motion artifacts. Thus, a system is needed that reduces patient discomfort and motion artifacts in resulting images.
Heretofore, CTA and EBA systems have been unable to obtain moving images of the coronary arteries and more generally moving angiography. A series of images (2-D or 3-D) illustrating changes in an object with respect to time is referred to as a cine image. Conventional CTA and EBA systems have been unable to offer cine angiography. Thus, there is a need for an angiography imaging method and apparatus for reconstructing a sequence of two- or three-dimensional images that show the motion of coronary arteries during a cardiac cycle. Additionally, current imaging methods require a lengthy period to acquire images. The time period required to acquire coronary arterial images is often too lengthy for the comfort of a patient. Thus, a need exists for a method and apparatus for imaging coronary artery motion and cardiac activity in a short time window for accurate imaging and patient comfort. Further, current imaging methods result in gaps and poor resolution in the resulting three-dimensional image due to the reconstruction techniques used, such as retrospective gating and other image reconstruction techniques, for example. Thus, there is a need for an imaging method and apparatus for improved quality imaging for angiography and motion in a cardiac cycle.